Microvascular Flow Velocimetry in Human Tendons

Tendon injuries are common in sports and physically demanding occupations. Conventional ultrasound methods, such as power Doppler (PD), indicate that healthy tendons are largely avascular; however, invasive techniques have revealed the presence of microvasculature in these tendons. The vascularity visualized in injured tendons through PD likely represents only a fraction of the underlying problem. This paper hypothesizes that the SUper-Resolution ultrasound imaging using Erythrocytes (SURE) can resolve subwavelength-size tendon microvasculature and flow characteristics within three seconds of data acquisition. Human tendon data were acquired by a Verasonics Vantage 256 scanner and a GE LOGIQ E9 scanner using a 10-MHz GE L8-18iD probe with a transducer fixture to minimize motion. The theoretical wavelength, λ, was 154 µm. SURE imaging resolved vessel widths down to 43.9 µm (≈ λ/3.5) and was able to separate vessels with a center-to-center distance of 68.3 µm (≈ λ/2.3). The estimated velocity of these vessels ranged from 2.3 to 3.3 mm/s. The improved sensitivity of SURE in detecting microvasculature suggests its potential for detecting slow blood flow in diseased tendons for potential early diagnoses.